Velocity Measurement of Gas–Liquid Slug Flows Using Multichannel Ultrasonic Doppler Sensor System

Horizontal gas-liquid slug flows are widely encountered in important industrial processes. Bubble velocity measurement is of great significance for understanding the heat/mass transfer and flow pattern transitions, and thus optimizing the industrial processes. Multiscale bubbles in slug flow are characterized by complicated interactions and thus exhibit intricate transient behaviors, making the velocity measurement exceedingly challenging. In this study, a multichannel ultrasonic Doppler sensor (MCUDS) is proposed to measure the bubble velocities in gas-liquid slug flows. The MCUDS features region-focused characteristics and thus yields high sensitivity at different measurement depths. A field programmable gate array (FPGA)-based measurement system is designed to generate pulse ultrasonic signals and implement rapid and stable data acquisition, processing, and transmission. A Taylor bubble tracking method based on the effective information ratio is proposed to measure the velocities of the nose and tail of Taylor bubbles. Doppler pulse repetition method (DPRM) with a sliding window is combined with the expanded autocorrelation (EAC) algorithm to derive the Doppler shift. The research results indicate that integrating a sliding window into the DPRM effectively improves the temporal resolution of bubble velocity measurements, thereby accurately constructing the spatiotemporal distribution of the velocity vectors of dispersed bubbles. This allows for the revelation of the complex motion processes of bubbles and the slug aeration characteristics under different gas-liquid flow conditions.